The invention relates to a device for controlling the rotation of the working rollers in a tube rolling mill, more particularly for reducing mills or sizing mills of the kind comprising a number of housings having three working rollers normally disposed in axial alignment on a single bearing structure, the rollers in each housing being keyed to corresponding shafts controlled from outside the housing and actuated by a single motor.
In the rest of the description and in the accompanying claims:
The term "rolling mill" denotes either a tube-reducing mill or a tube-sizing mill;
The terms "high-speed shaft," "high-speed gear," "high-speed bevel gear and pinion" have the usual meanings in the art, i.e. respectively denote a shaft, a kinematic gear and a pair of bevel wheels, all of which rotate at the same speed as the motor associated with the rolling-mill, and
The terms "slow shaft," "slow gear," "slow bevel gear and pinion" have the usual meanings in the art, i.e. respectively denote a shaft, a kinematic gear or a pair of bevel wheels which are kinematically connected to the rolling-mill motor via a speed reduction gear.
Hitherto the rotation of the working rolls in each housing in a rolling mill of the aforementioned kind has been controlled from a single motor associated with the rolling-mill, basically by means of the following two systems:
Use of a single reduction unit for all the rolling-mill housings, the unit comprising slow gears (slow bevel gears and pinions) for each housing, i.e. for each roller, or
Use of a reduction unit for each single housing, the unit being connected to the rolling-mill motor via high-speed gears and connected to the individual rolls in each housing via slow gears.
The main disadvantage of the aforementioned prior-art control systems is that a gear having a low speed and therefore a high torque is required for each working roll in each housing.
Other disadvantages are that each housing bearing has considerable size and weight, and the distance between the axes of adjacent housings is difficult to reduce to the optimum technological value. Another serious disadvantage is the complexity and difficulty of the maintenance operations periodically required on the housing bearing, or the adjustment of the bearings themselves.